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BGP Fundamentals

Chapter Description

In This sample chapter from Troubleshooting BGP: A Practical Guide to Understanding and Troubleshooting BGP, the authors cover BGP Messages and Inter-Router Communication, Basic BGP Configuration for IOS, IOS XR, and NX-OS, IBGP Rules, EBGP Rules, and BGP Route Aggregation


BGP is a powerful path vector routing protocol that provides scalability and flexibility that cannot be compared to any other routing protocol. BGP uses TCP port 179 for all BGP communication between peers, which allows BGP to establish sessions with directly attached routers or with routers that are multiple hops away.

Originally, BGP was intended for the routing of IPv4 prefixes between organizations, but over the years has had significant increase in functionality and feature enhancements. BGP has expanded from being an Internet routing protocol to other aspects of the network, including the data center.

BGP provides a scalable control-plane signaling for overlay topologies, including MPLS VPNs, IPsec SAs, and VXLAN. These overlays can provide Layer 3 services, such as L3VPNs, or Layer 2 services, such as eVPNs, across a widely used scalable control plane for everything from provider-based services to data center overlays. Every AFI / SAFI combination maintains an independent BGP table and routing policy, which makes BGP the perfect control plane application.

This chapter provided a fundamental overview of BGP from a session perspective, as well as route advertisement behaviors for IPv4 and IPv6 protocols. Networking vendors continue to use BGP for new features, and having the ability to effectively troubleshoot BGP is becoming more and more necessary.

This book provides emphasis on various BGP-related problems that are encountered in real-life deployments, which have caused major outages to the network over the years.

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